88 300E low idle problems after fuel pump fix - Page 4 - PeachParts Mercedes-Benz Forum

benzborg · #46 04-05-2010, 12:32 PM

Quote:

Originally Posted by Cal Learner

Don't rule out the CPS. As slk230 says, the CPS will give you the precise no-spark symptom you're experiencing. That's because the CPS tells the ignition system when to spark for proper fuel ignition. No signal, no spark. That seems particularly likely, in view of the fact that you've already swapped known good ECU and coil with no change in symptoms.

As for the voltage reg, I don't think that plays any role, because it isn't operating until the motor is running. You're starting the motor on battery power, not on alternator/vr power.

EDIT: Sorry, the alphabet soup got me until I just re-read the post. I was thinking EZL when I referred to ECU above. My point there was that the CPS works in tandem with the EZL (ignition control unit), so if CPS and coil are both known good but still no spark, the EZL may be on the fritz. There, I think I'm writing what I'm thinking.

Well I went back at it this morning w/o luck. I did notice the tach needle bounce a few times at various cranking sessions until my battery got weak.
The CPS seems to be doing it's thing - so I've hit bottom. Perhaps I shouldn't have touched the ECU at all although after swapping the day it last ran everything seemed fine. It was after I parked it and came back out - it fired up for less than a minute and quit. Dead ever since. Does that tack needle moving while cranking tell us anything? I've never seen that happen before.

benzborg · #47 04-05-2010, 05:38 PM

Back at it I've found no voltage at the coil with key in the on position without cranking. A call to a local Benz guy told me to swap the EZL with the one from the working car. The other suggestion was the key ignition switch itself, although I get all dash lights in the on position. This is sure a drag but oh well. No voltage to the coil - what's that indicate other than a dead 300E?

benzborg · #48 04-08-2010, 04:16 PM

I got the beast running finally with a new distributor cap and wires. After all the swapping with used parts what I should have done in the first place was the fix. Thanks input to my questions. The car is still idling quite low with any OVP I have which work well in the other car.

Question. Is there actually some adjustment that can be done on the the
plastic adjustment screw of the microswitch or can a few RPMs be gotten by adjusting the linkage? I'm not sure I can even see the screw on the microswitch from top view. Recall my duty cycle readings were 3.65V with key in the on position and 6.8V at idle, with no change at 2500 RPMs with no change swapping ECU with the working car. The last sensor I think must be replaced because my e-test was so far out of whack is the O2 sensor.

According to the guy at the e-test facility advising me the cat is shot as per to his measurements likely caused that failed readings but I'm sure a new O2 sensor wouldn't hurt.

slk230red · #49 04-08-2010, 11:20 PM

Quote:

Originally Posted by benzborg

I got the beast running finally with a new distributor cap and wires. After all the swapping with used parts what I should have done in the first place was the fix. Thanks input to my questions. The car is still idling quite low with any OVP I have which work well in the other car.

Question. Is there actually some adjustment that can be done on the the
plastic adjustment screw of the microswitch or can a few RPMs be gotten by adjusting the linkage? I'm not sure I can even see the screw on the microswitch from top view. Recall my duty cycle readings were 3.65V with key in the on position and 6.8V at idle, with no change at 2500 RPMs with no change swapping ECU with the working car. The last sensor I think must be replaced because my e-test was so far out of whack is the O2 sensor.

According to the guy at the e-test facility advising me the cat is shot as per to his measurements likely caused that failed readings but I'm sure a new O2 sensor wouldn't hurt.

Thanks for posting what you found. Yes, it's always better to eliminate the simple items first; rotor, distributor cap, spark plug wires, non-resistor spark plugs, etc.

The micro-switch is not adjustable, it either works or it doesn't. Just make sure the contact is closed at idle.

Also, inspect the vacuum hoses on both sides of the Idle Control Valve to make sure that they are securely connected and also not cracked.

You should check your 'Duty Cycle' and adjust if necessary, but I would replace the O2 sensor first if you suspect it's defective.

Glad you got it running.

benzborg · #50 04-11-2010, 01:23 AM

Quote:

Originally Posted by slk230red

You should check your 'Duty Cycle' and adjust if necessary, but I would replace the O2 sensor first if you suspect it's defective.

Glad you got it running.

Thanks again for questions answered.

Running rough is better than being parked. Thanks and I'll see if any adjustment might improve a few bugs (rich and using lots of fuel) and let you know what numbers we get soon.